Exemplary embodiments of the invention relate to a method and an installation for processing raw liquid manure and/or fermentation residues from biogas production.
It is known that a solid phase and a treated liquid phase are produced in the separation of raw liquid manure and/or fermentation residues with a solid bowl scroll centrifuge. While in the separation of raw liquid manure the solid phase can be utilized, for example for biogas production, it would be desirable to further simplify the disposal of the treated liquid phase. In accordance with the invention this would be possible if the liquid phase were to contain still less suspended matter and ultrafine particles and the COD value (chemical oxygen demand) of the treated liquid phase could be lowered. According to the state of the art such treatment has hitherto not been possible, or only with very high expenditure, and accordingly exemplary embodiments address such deficiencies of conventional techniques.
Accordingly, exemplary embodiments of the present invention are directed to a method and a device for processing raw liquid manure and/or fermentation residues from biogas production, which allows simpler disposal of the treated liquid phase.
According to the invention, a method for processing raw liquid manure and/or fermentation residues comprises the following steps: provision of raw liquid manure and/or of fermentation residues; treatment of the raw liquid manure and/or the fermentation residues in a first treatment stage with formation of a first solid phase and a first treated liquid phase; preconditioning of the first treated liquid phase; and treatment of the first treated and preconditioned liquid phase in a second treatment stage with formation of a second solid phase and a second, further treated liquid phase.
Through the further removal of the ultrafine particles or suspended matter as a result of the preconditioning, the COD content of the second treated liquid phase compared to the first treated liquid phase is lowered so far that introduction into a biological stage of a treatment plant becomes possible. The COD value (chemical oxygen demand, particularly in mg/l) is a measure of the sum of all organic compounds in water, including the compounds difficult to degrade.
Here the preconditioning can advantageously and simply be effected in the first step by addition of a flocculant and/or alteration of the pH. This serves for the formation of larger solid particles by flocculation.
Also, during the addition of the flocculant it is advantageous if in the second step a further addition of a flocculation aid is effected to improve the shear strength of a coagulate. Due to the better shear strength, the coagulate can also be exposed to higher centrifugal forces and be better separated from the first (pre-)treated liquid phase by a further treatment process.
It is advantageous if the treatment of raw liquid manure or the fermentation residues in the first treatment stage in step ii) is effected by a centrifuge, in particular a solid bowl scroll centrifuge. Admittedly, a screw press can also be used for dewatering the raw liquid manure. However, it has been found that slimes can be particularly effectively removed from the clarified phase through the use of a centrifuge, whereas with use of screw press, these slimes predominantly remain in the first treated liquid and complicate its treatment in the second treatment stage.
In order to facilitate the biological degradability of the second solid phase, it is advantageous if the flocculation aid is a water-based polymer.
The first solid phase obtained in step ii) can be used for example for the production of biogas or as a phosphate-rich manure.
The second treated liquid phase advantageously has a decreased COD value relative to the first treated liquid phase. A low COD value of a liquid results in a lower burden on its introduction into a treatment plant. The second solid phase can also be used in many ways, such as again for biogas production or as phosphate-rich manure.
According to the invention, an installation for processing raw liquid manure and/or fermentation residues comprises at least one first centrifuge, in particular a solid bowl scroll centrifuge, for dewatering raw liquid manure with formation of a first treated liquid phase and a first solid phase and a first metering device for the addition of a flocculating agent to the first treated liquid phase or an agent for altering the pH of the first treated liquid phase.
The addition of a flocculant to raw liquid manure is already known. However, such an addition raises the chemical burden of the first solid phase. Apart from this, in spite of the addition of a flocculant, there is often a considerable content of ultrafine particles in the first treated liquid phase. On the other hand, the addition of the flocculant or a means for altering the pH to the first treated liquid phase, i.e. only after the first treatment stage, enables the obtention of a very largely ultrafine particle-free clarified phase by mechanical treatment in a second treatment stage.